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Nature of Science

Performance Benchmark N.12.A.6
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Nature of Science
Scientific Inquiry


Science, Technology, and Society
Content Areas
Nature of Science (NOS)
Life Science
Earth Science
Physical Science

Students know organizational schema can be used to represent and describe relationships of sets. E/S

Humans are bombarded with information constantly.  It is human nature to organize this information into units based upon similarities and differences to decipher patterns, apply meaning, and draw conclusions.  For example, books can be separated into non-fiction and fiction. The non-fiction books can be further divided into more specific topics such as sports, nature, or social sciences. The Dewey Decimal System was designed to apply order to an ever expanding world of knowledge.  It divides book topics into ten main numeric categories.  Each category is further divided into ten subcategories which are divided into ten subdivisions.  For example, all of the 500s represent science topics, the 570s represent life sciences, and 577 is where you would find books about ecology.  By understanding the classification schema of the Dewey Decimal System, anyone can easily access desired information held within a library.  The internet has been growing nearly exponentially since its inception.  The information in the internet also has an overlaying organization schema.  Imagine how long it would take to find the answer to “How tall is a coastal redwood?” if you had to look through each file on the internet one at a time.  As of February 2007, the Netcraft Web Server Survey found over 108 million distinct web sites, with 29.7 billion web pages ( Figure 1 shows how the organization of the internet is expressed in an URL (Uniform Resource Locator) address. 

Diagram that disects a URL, naming each part of the web address.
Figure 1. A URL dissected. (from

In science, the objective of all classification systems is to orderly arrange a large array of objects so that their differences and similarities can be better understood.  Classification schema can facilitate the development of hypothesis, theories, and conclusions.   For example, classification allows scientists to set boundaries to their research by defining which groups are included or excluded from the study. It also allows scientists to identify patterns within a data set, allows for extrapolation, and facilitates the communication of results within the framework of a defined classification system.  All fields of science utilize classification schema.  For example, biology classifies species into kingdoms, chemistry classifies matter within the periodic table, physics classifies energy, and earth science has a classification system of minerals and rocks.

Scientists have identified approximately 2 million species on Earth and estimate that there may be as many as 40 million species.  Early classification systems separated the known species as either a plant or animal and further defined animals according to their form of locomotion. Aristotle classified animals in groups based upon if they could walk, swim, or fly.   This early system had limitations that were hard to overcome.  For example, how would birds like penguins that swim or ostriches that walk be classified?  Carolus Linnaeus (1707-1778) published his Systema Naturae where he proposed an entirely new way to classify plants, based on their reproductive systems.. Linnaeus’ system was very practical and usable compared to previous classification systems.  His naming method, binomial nomenclature, was later adapted to classify all life forms.  But classification of species is now based on their evolutionary relationships, determined by genetics, biochemistry, and morphology.  Recall, the first classification system organized life forms into two groups (plant or animal).  Figures 2 shows how this classification system was modified as biologists learned more about the differences between the various life forms. The two kingdom (Plantae and Animalia) system was expanded to three kingdoms, then to the traditional five kingdom system.  Current comparative genetic studies have allowed biologists to recognize important distinctions between bacteria and archaea which led to the proposal of a sixth kingdom system.  Figure 3 shows an example of the classification of a single species from kingdom to species. 

Figure 2. The division of life forms into kingdoms has been modified several times.


Figure 3. An example of the classification of a single species.


The periodic table is used in chemistry to compactly show relationships between elements.  The periodic table was developed in 1869 by Dmitri Mendeleev to present all the elements in a way that shows their similarities and differences.  Columns represent elemental groups which have similar chemical properties.  For example, the first column is the alkali metals.  Alkali metals are soft, extremely reactive metals, react with water to form hydrogen gas, and form +1 ions.  In addition to groups, the periodic table is arranged in rows (periods), blocks (based on electron configuration), and metal/metalloids/non-metals zones.   Another level of organization within the periodic table is the chemical trends.  For example, the atomic radius of an atom decreases as you go across a period.  Understanding the layers of information provided in the periodic table, a chemist knows the main properties of each of the groups in the periodic table and how chemical properties vary within a group. They can also predict the properties of any particular element with a reasonable degree of confidence.  Figure 4 shows an early version of the periodic table and Figure 5 provides a current version of the table.  This classification schema has evolved through time and will continue to evolve as new information is discovered.

Mendeleev.gif (28713 bytes)
Figure 4. Dmitri Mendeleev’s 1872 periodic table.

Figure 5. A current Periodic Table. (from


Energy may be classified as radiant, chemical, or thermal. This is not the only classification schema accepted.  Energy can also be classified solely as potential or kinetic forms each expressed more specifically as electrical, mechanical, chemical, or thermal.  A third schema is more delineated as illustrated in Figure 6.  This is an example of how multiple classification systems can be designed to meet the purpose of the user.


Figure 6. An example of how a classification system of the same information can be simple (third column) or complex (middle column) depending on the needs of the user.

The example in Figure 6 shows how each of the schema separate the types of energy into categories based on similarities in properties and then these global groups can be further divided based on more specific group definition.  For example, the electromagnetic spectrum (Figure 7) was constructed to illustrate how radiant energy is classified by wavelength. The long wavelengths equals radio waves while very short wavelengths are defined as gamma rays.  Wavelengths between 400 and 750 nm are classified as visible light which can be further delineated into colors (500-570nm = green) (Figure 8).

The electromagnetic spectrum: Radio waves, microwaves, x-rays, gamma rays, and the spectrum of visible colors are all really the same thing - electromagnetic energy.
Figure 7. The electromagnetic spectrum. (from


Figure 8. The electromagnetic spectrum showing the wavelengths of visible light.

Earth Science
Earth Science also uses a classification schema to organize a large body of accumulated knowledge about minerals.  There are approximately 3800 known minerals.  While this is not as cumbersome as classifying an animal, it would be near impossible to classify an unknown mineral sample if an organizational system was not in place.  The classification schema for minerals can be adapted into a mineral identification key that uses the process of elimination to classify an unknown sample.  For example, you can use the table in Figure 9 to identify an unknown mineral sample provided that your sample is one of the 11 minerals described in this table.  You would first observe if your mineral exhibits cleavage or fracture.  Then you would determine the streak color and continue to test the properties given in the table in order from left to right using process of elimination to narrow down the possibilities till your arrive at your mineral name.

Figure 9. An identification table for 11 metallic to submetallic minerals.

Dichotomous Keys
A dichotomous key is a tool designed by scientists to identify something unknown.  Keys may list a series of statements organized into couplets (Figure 10).  For example, one could use the dichotomous key in Figure 10 to differentiate between four species of birds.  Let’s try to identify Bird X.  When using a key, always start at couplet number 1.  Does bird X have a beak that is relatively long and slender or stout and heavy?  “b” is the correct choice so we go to step 2.  Is the bottom surface of the lower beak of Bird X flat and straight or curved?  Again, “b” is the correct choice.  Go to step 3.  Finally, does the lower edge of the upper beak have a distinct bend or is it mostly flat?  Again, “b” is the correct choice.  We have identified Bird X as Platyspiza.

Figure 10. A typical dichotomous key.

A dichotomous key may also be presented in pictorial form with paired choices (Figure 11). The user must choose between the two options given and follow the path through the key to the correct name of the unknown through the process of elimination.


dichotomous key answers
Figure 11.  A pictorial dichotomous key.  The user would use this key to identify a type of matter.  The first choice by the user is whether their unknown is a substance or a mixture.

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Performance Benchmark N.12.A.6

Students know organizational schema can be used to represent and describe relationships of sets. E/S

Common misconceptions associated with this benchmark:

1. Students incorrectly believe that each classification schema is static.
Any designed classification schema must be flexible to allow the addition of newly discovered items or relationships.  This flexibility not only applies to reorganization of existing pieces but extends to the addition of completely new categories if something truly novel is discovered.  This idea of an active and adaptable framework not only holds true for classification schema but applies to all aspects of science.  By its very nature, science evolves as new observations and/or reinterpretations of previous observations.

For greater detail on the nature of science, see the American Association for the Advancement of Science (AAAS) Benchmarks for Science Literacy On-Line at


2. Students inaccurately believe that there is only one classification schema per discipline.
As discussed above, many classification schemas may be designed to classify the same data set to meet the needs of the user.  It may be extremely simple if only global differences are important or complicated if more specificity is needed.

Again, for greater detail on the nature of science, see the American Association for the Advancement of Science (AAAS) Benchmarks for Science Literacy On-Line at

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Performance Benchmark N.12.A.6

Students know organizational schema can be used to represent and describe relationships of sets. E/S

Sample Test Questions

1st Item Specification:  Recognize that each branch of science has developed classification systems based on observable characteristics.

Depth of Knowledge Level 1

  1. Which group of terms is in the correct order from the most general to most specific when classifying organisms?
    1. Kingdom, phylum, genus, species
    2. Species, phylum, genus, kingdom
    3. Genus, species, kingdom, phylum                                   
    4. Phylum, kingdom, species, genus
  1. Which statement BEST illustrates a classification system?
    1. A glacier melts at the rate of one meter per year.
    2. Ocean depths are measured by using sonar.
    3. Snowfall predictions for winter storms vary.
    4. Stars are grouped according to their color.

Depth of Knowledge Level 2

  1. Which property was most likely used to classify the substances below?
Group A Group B Group C


i ron 
water vapor
    1. Abundance within the Earth
    2. Specific heat
    3. State (phase) of matter
    4. Chemical composition
  1. The USDA soil classification chart below is used to classify soils based on particle size.  Use this diagram to answer the following question.

Classification of soil texture by percentage of clay, sand and silt

    What type of soil has 50% clay, 30% silt, and 20% sand?
    1. Loam
    2. Silt loam
    3. Clay
    4. Silty clay loam

2nd Item Specification:  Explain that scientists use various classification systems to organize information.

Depth of Knowledge Level 1

  1. A student is given a set of objects and is asked to construct a classification scheme to explain the relationship between the objects.   A classification system should be based on
    1. interpretations.
    2. observations.
    3. hypotheses.
    4. inferences.
  1. The diagrams below represent various geologic cross sections.

(From ExamGen 4.3)

    Which of the following skills will a scientists use to organize information like the geologic cross sections above?

    1. Classification  
    2. Prediction
    3. Observation
    4. Measurement

Depth of Knowledge Level 2

  1. Keys are used by biologists to accurately classify unknown organisms such as the unidentified female mosquito shown in the diagram below.  These keys are designed to categorize organisms according to structural characteristics.  The key shows various characteristics used to identify the difference between Anopheles, Deinocerites, Culex, Psorophoro and Aedes mosquitoes. 

From ExamGen 4.3

    According to the key, which characteristic distinguishes a male from a female mosquito?
    1. Antennae appearance
    2. Palp length
    3. Leg scales
    4. Abdomen points
  1. The Periodic Table of known elements is a tool used by chemists that exhibits many levels of organization.  Use the periodic table to answer the following question.


    Electronegativity is a value that expresses the ability of an atom to pull electrons towards itself.  A periodic pattern of electronegativity is expressed as follows:
    1. Electronegativity increases as you go across the periodic table.
    2. Electronegativity decreases as you go down the periodic table.
    Which of the following elements has the highest electronegativity?
    1. Sulfur (S)
    2. Chlorine (Cl)
    3. Selenium (Se)
    4. Bromine (Br)

3rd Item Specification:  Explain that classification systems can be modified over time to account for new information.

Depth of Knowledge Level 1

  1. Classification tools, like the periodic table or binomial nomenclature, are
    1. generally accepted by all scientists who are experts.
    2. modified if necessary as new data and observations are collected.
    3. not modified once completed if based on careful experimentation.
    4. generally only accepted if scientists agree with collected data.
  1.  While conducting careful experimentation, a chemist discovered a new element.  Chemists would
    1. ignore the new data because it did not fit into the generally accepted periodic table.
    2. create a new classification system with the new information.
    3. disagree on how to incorporate the new data and create many classification systems based on personal preference.
    4. modify the current periodic table to include the new data.

Depth of Knowledge Level 2

  1.   The table provides a fictional scheme to classification of four Orders of animals. Use this fictional scheme to answer the following question.






Food source





Number limbs











Live birth



Live birth

Temperature regulation





Outer layer





    A wildlife biologist discovers an animal that is an herbivore with four limbs, has sharp teeth, lays eggs, is endothermic, and has scales.  Which order does this animal belong to?
    1. Order B because the animal has sharp teeth, lays eggs, and is endothermic.
    2. Order C because the animal is an herbivore, lays eggs, and has scales.
    3. A new order named B/C was created to better describe the new animal.
    4. A new order named C/D was created to better describe the new animal.
  1. Dimitri Mendeleev proposed the following periodic table in 1869.  This periodic table arranged the known elements (in 1869) by increasing atomic mass and then by physical properties.


    A chemist discovers an element with an atomic mass of 210.  Which of the following proposes a likely placement into Mendeleev’s periodic table?
    1. Group III, Period 9
    2. Group VII, Period 10
    3. Group I, Period 12
    4. Group VI, Period 11

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Performance Benchmark N.12.A.6

Students know organizational schema can be used to represent and describe relationships of sets. E/S

 Answer to Sample Test Questions

  1. A, DOK Level 1
  2. D, DOK Level 1
  3. C, DOK Level 2
  4. C, DOK Level 2
  5. B, DOK Level 1
  6. C, DOK Level 1
  7. A, DOK Level 2
  8. B, DOK Level 2
  9. B, DOK Level 1
  10. D, DOK Level 1
  11. C, DOK Level 2
  12. D, DOK Level 2

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Performance Benchmark N.12.A.6

Students know organizational schema can be used to represent and describe relationships of sets. E/S

 Interventions and Strategies and Resources

The following list of intervention strategies and resources will facilitate student understanding of this benchmark.


 1. Classification quiz from The Open Door Web Site

Students need to be given a set of 12 pictures of unknown species.  They then use the key provided at this site to classify each one.  Students can then click on the “Wise Owl” and take a classification quiz. 

To access this introduction to classification skills activity, go to

2. “Classifying and Sequencing Activity” from the National Health Museum

This website provides a series of activities to meet the objectives below.  It is not web-based, but it gives students experience in making observations, grouping objects based on similarities, and constructing a multistage and serial classification schema.

Objectives of this activity include;

  1. To identify properties that can be used to classify in a binary classification system;
  2. To construct a multistage (dichotomous) classification system for a set;
  3. To identify properties by which a set can be ordered in a serial fashion and order a set accordingly.”

To explore this activity, visit


3. “Potato Chip Classification Activity” from the Educator’s Reference Desk

This is another classroom activity that provides students with experience classifying objects based on similarities.  This activity allows students to classify objects that they are quite familiar with…Potato Chips!

For a printable copy of this lesson, go to


4. “Classifying Chemicals Using Properties Activity” from Chemistry and You!

While engaged in this activity, students examine samples of unknown substances with the purpose of classifying them as either a mechanical mixture, a solution, or a pure substance.

To access this activity, visit


5. “Planet Categorization: What is a Planet?” Activity from PBS

This is not a web based activity, but it is a lesson plan with all handouts provided.  Centered in this activity is the Pluto debate and application of the definition of just what it means to be a planet. 

The objectives for the lesson include;
      1. To apply astronomy concepts to develop and test a classification system for planets.
      2. To participate in a class vote on planet classification.
      3. To read an article about astronomers' response to the planetary categorization.
      4. To discuss and write an essay about the scientist's role as decision-makers for the public.”

For all of the supporting materials for this activity, go to

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